fix: accept comands with leading and trailing white spaces (#1200)

[ti-srebot]

cherry-pick #1200 to release-2.0

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What problem does this PR solve?

exit with trailing white spaces

» exit
Error: unknown command "exit" for "dmctl"
Run 'dmctl --help' for usage.
fail to run: [exit]

exit with leading white spaces

»  exit
Error: unknown command "exit" for "dmctl"
Run 'dmctl --help' for usage.
fail to run: [exit]

What is changed and how it works?

remove leading and trailing white spaces before handling it.

Check List

Tests

• Manual test (add detailed scripts or steps below)
  • re-run commands above

Code changes

Side effects

Related changes

• Need to cherry-pick to the release branch

[csuzhangxc]

LGTM